Male black widow spiders overwhelmingly prefer their female mates to be well-fed virgins, according to new research from UTSC professor Maydianne Andrade and PhD student Emily MacLeod. (Photo by Ken Jones)

New UTSC research shows that male black widow spiders prefer their
female mates to be well-fed virgins, revealing a rare example of mate
preference by male spiders.

The study, authored by UTSC post-doc Emily MacLeod and Maydianne
Andrade, a professor in UTSC’s Department of Biological
Sciences, found in both controlled field studies and the wild that
males overwhelmingly chose to mate with well-fed, unmated females.
They also found male black widows can tell whether a potential mate is
well-fed and unmated by pheromones released by
females.

“This near unanimous preference by males for well-fed mates
using only phermonal cues has not been documented in any other spider
species,” says MacLeod. “These are not visual or auditory
cues they are picking up but smells they are sensing, often from far
away.”

Macleod says the reason males show a strong preference for females
who smell like they’ve eaten a lot is that mating with a fatter
female may result in more offspring than with less well-fed
females.

“Females who have been able to eat a lot and obtain a lot of
food resources can transfer those resources into egg
production,” says MacLeod. “It’s not just that they
are healthier but that they are more fertile because they can produce
more egg sacks.”

Another reason for male choice may be a simple matter of survival.
“It’s important to remember that when a female eats a lot
of prey, she’s less likely to eat a potential mate,” says
Andrade.

The study focused on Latrodectus Hesperus, a species of
black widow native to western North America including parts of
Canada.Theseblack widows are not generally
cannibalistic but males are much smaller than females, meaning if a
female is hungry her drive to feed will be greater than her drive to
reproduce. “If you have this little food item dancing on a web
you may as well eat it if you don’t have energy to produce
eggs,” adds MacLeod.

The existence of male choice in nature is unusual because of the
costs associated with being picky. In a lab environment male spiders
can afford to be choosey, but in nature there are risks in spending
time, energy and resources finding a mate, says Andrade.

The study also shows there may be more involved to mating
preference than a mere matter of what’s available. “It
shows that males aren’t just promiscuous sperm packages, in fact
they can go to great lengths to exercise choice in a mate,” says
MacLeod.

The research,
which received funding through an NSERC Canada Graduate Scholarship
(CGS), is published in the journal Animal Behaviour.

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